We are studying the regulation of gene expression in the preimplantation bovine embryo. Maternal to embryonic gene activation is one of the most important events in embryo development. Even though embryo gene activation in bovine has been proposed to occur at late 4 cell stage, the details of the activation, regulation of the timing of gene expression and the genes that are involved in activation are not clearly understood. The main purpose of this project is to determine at what cell stage embryonic genes are activated and what the players ar~ in this activation process; e.g. mechanism (s) of the regulation.. We will use confocal nucroscopy to identify the appearance of specific gene products in staged embryos.